1. Field of the Invention
This invention relates to an electrophotographic member capable of yielding an image of good quality incorporating a metallocene compound in a protective layer provided on the surface of a photoconductive layer.
2. Description of the Prior Art
A number of photosensitive members have been practically applied in electrophotographic systems including processes comprising charging, exposing and developing procedures (see, for example, U.S. Pat. No. 2,297,691). For example, known photosensitive members include those which include a layer of organic photoconductive material directly formed on a conductive substrate by coating or vacuum deposition or those in which the organic photoconductive material is combined with an organic polymeric binder, those using inorganic photoconductive materials such as ZnO, CdS, TiO.sub.2 and the like dispersed in a binder, those using vacuum-evaporated amorphous selenium and its alloys, and those wherein different types of photoconductive layers are superposed on one another (see, for example, Japanese Patent Publication Nos. 5394/70, 3005/71 and 14271/74). In order to ensure certain levels of both electrical and optical properties and mechanical properties or to improve and stabilize these properties, or in some cases to improve the characteristics required in a developing process, it has often been proposed to provide a protective layer on the photosensitive member surface.
Electrophotographic members having a surface layer on a photoconductive layer have been known in the art. One type of such surface layers is an electrically insulating surface layer composed of a highly electrically insulating material (e.g., see Tanaka, et al., U.S. Pat. No. 3,438,706 and Watanabe, et al., U.S. Pat No. 3,457,070). This is advantageous in that the thickness of the electrically insulating surface layer can be thickened and in that materials having high mechanical strength can be used. However, in order to repeatedly use an electrophotographic member with this type of surface layer, a specific latent image-forming process is required, such as: (A) first charging; second charging with an opposite polarity to that of the first charging; and imagewise exposure; or (B) first charging; second charging with opposite polarity and simultaneous imagewise exposure; and entire exposure, is required. Furthermore, the use of such a surface layer requires two or more charging steps per one copying step, which results in complicating the apparatus, unstable properties, and high production costs.
Another type of such surface layers is a protective layer composed of a relatively low electrically insulating material, i.e., a material having a low electric resistance. (See Joseph, U.S. Pat. No. 3,434,832 and Polastri, U.S. Pat. No. 4,006,020.) In most cases, however, the use of such a protective layer causes a high residual potential, and a great increase of cycle is required. These electric variations result in scumming and do not result in a clear reproduction image.
In order to avoid such problems, an additive has been incorporated in the protective layer or a single protective layer of a specific type has been used. However, most of these techniques have involved problems such as a loss of transparency which is essential to a protective layer, a loss of image sharpness under high humidity conditions or fogging in the background under low humidity conditions, a reduction in charging property of a photoconductive layer, and a cyclic build-up of residual potential, and can thus not be put into practice. This is because these methods have been directed merely to lowering the electric resistance of the protective layer or to improving its humidity dependence. In order to stabilize and ensure the charging property of the entire photoconductive layer over a long period of time under all practical conditions, various characteristics such as transport, injection and residence of the electric charges occurring on the surface of a protective layer and at the interface between the photoconductive layer and the protective layer must be collectively controlled. It is difficult to find a material which can improve these characteristics while controlling the electrical conductivity of the protective layer and which exhibits stable characteristics with variations in humidity and temperature. There has never been known a material, which when contained in a binder resin can satisfy the above-mentioned characteristics, and provide the mechanical strength necessary to meet the requirements of an ordinary protective layer.